EGOR

[Ludis Langens]

Robert Harris wrote:
> 
> Stoic is determined primarily by the fuel and little else.  The others vary
> considerably from engine to engine, altitude, temperature etc.  Both are
> determined empirically from actually tuning the engine and optimizing the
> results.  In other words - they are not magic numbers.
> 
> If you record the ego output at these two points, you have a nice means of
> getting back to these points.  The actual numbers are meaningless - as long as
> they are repeatable and of usable scale.
> 
> Precision is a fruitless anal exercise in futility.  At either point you can
> vary the mixture a few percent and the difference will be lost in statistical
> noise.
>
> [...]
>
> Good enough self calibration for engine control and getting back to the best
> power points after they are determined by other much more accurate means.

The above ignores a useful ability of a wide band sensor.  Lets say you
have a new engine on a dyno.  The engine enters a poorly calibrated
range.  The injectors are firing for 5 ms.  Your wide band sensor says:
"15.8:1 AFR".  Your ECM can say: "Uh, oh, lets get the engine to stoich
to keep from melting pistons. "  The ECM does a bit of math (5 ms * 15.8
/ 14.7), and starts firing the injectors for 5.37 ms.  Ta-da, the ECM
was able to go from lean to near stoich in the time of a single
injection event.

With an old bang-bang style sensor, the ECM did this:  5 ms.  Uh, oh,
lean.  5.04 ms.  [10 or 20 ms later]  Uh, oh, still lean.  5.08 ms. 
Still lean.  5.12 ms.  5.16 ms.  5.2 ms.  5.24 ms.  5.28 ms.  5.32 ms. 
5.36 ms.  5.40 ms.  Oops, too rich.  5.38 ms.  5.36 ms.  5.38 ms. 
Meanwhile, the engine was running lean for a quarter of a second or more.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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